When you create a new profile property and check "Indexed" SharePoint will automatically create appropriate crawled property (after incremental or full crawl of user profiles) in format People:[Your property internal name].
From the UI you can only search for managed properties, so you should add a mapping between your crawled property and a managed property (or create it) through UI or PowerShell. From PoweShell it will following command:
$cp = Get-FASTSearchMetadataCrawledProperty -Name People:[Your property internal name]
$mp = New-FASTSearchMetadataManagedProperty -Name employeestatus -Type 1
New-FASTSearchMetadataCrawledPropertyMapping -ManagedProperty $mp -CrawledProperty $cp
And this is not the end. You should also modify CoreResultWebPart in search centre. This web part knows nothing about your new managed property, you should add it in config. Edit CoreResultWebPart in the search centre, find Display Properties->Fetched Properties and add <Column Name="employeestatus"/>.
Perform a crawl again (you might see an error that property doesn't exist), after this you can search using you property - employeestatus:"Hired". You can also modify xslt source of CoreResultWebPart to show value of this property on search UI.
Links:
Get-FASTSearchMetadataCrawledProperty
New-FASTSearchMetadataManagedProperty
New-FASTSearchMetadataCrawledPropertyMapping
Useful reading (you can skip metadata part) here
